This invention generally relates to slider-operated flexible zippers for use in reclosable pouches, bags or other packages of the type in which material, such as foodstuff, detergent, etc., may be stored.
Reclosable fastener assemblies are useful for sealing thermoplastic pouches or bags. Such fastener assemblies often include a plastic zipper and a slider. Typically, the plastic zippers include a pair of interlockable fastener elements, or profiles, that form a closure. As the slider moves across the profiles, the profiles are opened or closed. The profiles in plastic zippers can take on various configurations, e.g. interlocking rib and groove elements having so-called male and female profiles, interlocking alternating hook-shaped closure elements, etc.
Conventional slider-operated zipper assemblies typically comprise a plastic zipper having two interlocking profiles and a slider for opening and closing the zipper. In one type of slider-operated zipper assembly, the slider straddles the zipper and has a separating finger at one end that is inserted between the profiles to force them apart as the slider is moved along the zipper in an opening direction. The other end of the slider is sufficiently narrow to force the profiles into engagement and close the zipper when the slider is moved along the zipper in a closing direction. Other types of slider-operated zipper assemblies avoid the use of a separating finger. For example, U.S. Pat. No. 6,047,450 discloses a zipper comprising a pair of mutually interlockable profiled structures, portions of which form a fulcrum about which the profiled structures may be pivoted out of engagement when lower edges of the bases are forced towards each other by the moving slider.
Reclosable bags are finding ever-growing acceptance as primary packaging, particularly as packaging for foodstuffs such as cereal, fresh vegetables, snacks and the like. Such bags provide the consumer with the ability to readily store, in a closed, if not sealed, package any unused portion of the packaged product even after the package is initially opened. To gain acceptance as a primary package for foodstuffs, it is virtually mandatory that the package exhibit some form of tamper evidence to protect the consumer and maintain the wholesomeness of the contained product. In addition, in many cases it is necessary that food product be hermetically packaged. This may readily be accomplished by forming a plastic bag of a film having the appropriate barrier properties. However, where the bag is provided with a zipper, a problem arises in properly sealing the bag at the opening to be closed by the zipper, since the zipper itself does not provide a hermetic seal.
A resealable package that exhibits tamper evidence and can be hermetically sealed is disclosed in U.S. Pat. No. 6,354,738. The invention disclosed therein makes use of a strip having capped perforations or another form of weakening in a unique bag configuration. A bag is provided having front and rear walls joined along the bottom and sides and open at the top. A zipper is provided at the bag top having first and second zipper halves that include interlocking profiled closure members designed to interlock with each other. Each zipper half comprises a respective flange, each flange extending from below the respective profiled closure member toward the bag interior. The flanges are of unequal size with the shorter flange being sealed directly to one (first) bag wall. The longer flange is sealed to the other (second) bag wall and to the first bag wall below the point at which the shorter flange is sealed to the first bag wall. A tear line, such as a capped line of perforations of the type disclosed in U.S. Pat. No. 5,023,122, is provided in the longer flange between the locations at which it is sealed to the two opposing bag walls. The capped line of perforations or other tear line weakens the zipper flange so that it may be readily ruptured, without detracting from the barrier property of the zipper flange until rupturing actually occurs.
FIG. 6 of U.S. Pat. No. 6,354,738 shows a zipper having a so-called “split flange”, which name is derived from the fact that zippers of this tape can be manufactured by “splitting” a continuous web to form flanges. More specifically, such zipper tape is formed by extruding a pair of profiled closure members with a connecting membrane therebetween, forming a tear line near the center line of the connecting membrane, interlock the closure members and causing the connecting web to fold at the tear line, and then cutting or splitting the membrane on one side to form a short flange and a long flange, the latter having a generally V-shaped portion with the cusp at the tear line. Alternatively, the two zipper profiles of a split-flange zipper can be extruded separately, instead of being extruded as one piece and then cut. The split condition of the zipper flange results in faster and more consistent winding of the zipper on a spool as compared to the situation when the zipper has a continuous flange.
There is a need for a method of manufacturing the packages disclosed in U.S. Pat. No. 6,354,738, which discloses three-point sealing of the zipper, and other packages that employ four-point sealing of the zipper. Furthermore, during filling of resealable packages, it is important to avoid product contamination on the zipper flanges, which can result in poor seal quality of the finished product. In addition, it is important during sealing of the zipper flanges to the bag making film that the flanges not be sealed or tacked together. Also, in the case of resealable packages having a split-flange zipper, it is desirable that food product not become trapped behind the long zipper flange when the opened package is turned upside down and product is dispensed.